Communication systems are increasingly being required to provide a wide range of services, including different forms of information communicated and different communication characteristics. Information forms include voice, data, video, telemetry, and the like. Communication characteristics include quality, latency, reliability, cost, availability, portability, and the like. Infrastructure such as telecommunication systems, the Internet, and cable systems exist to provide long-haul routing and information content sourcing. However, difficulty remains in delivering this information to customers. This is particularly the case if the customer is located in a rural location, is communicating through portable equipment, or is mobile.
Traditionally, communication service providers have relied on copper wire or coaxial cable to connect distribution sites and subscriber premises. However, increases in the number of users, number and type of communication devices per user, and the information rate per device has strained the ability for traditional communication systems to provide the necessary bandwidth and flexibility. Various technologies including digital subscriber line (DSL) and video modems offer broadband access to the subscriber over existing copper or coaxial loop technologies. Fiber-to-the-home offers broadband access through additional wireline connections. While each technology has broadband delivery properties, each is subject to physical and signaling limitations that restrict availability in certain locations and for certain applications.
A promising technology is very-high-data-rate DSL (VDSL). A typical installation implements a hybrid local loop. Information packets are received and routed by a central office using ATM virtual circuits. The packets are sent from the central office over fiber-to-the-neighborhood (FTTN) to local optical network units (ONUS). Each ONU is connects to several customer premises over copper, such as unshielded twisted pair (UTP). A network interface device (NID) on the customer premises may format the information for customer premises equipment and isolate the customer premises from the VDSL network.
VDSL services may be symmetric or asymmetric. For example, downstream rates to the subscriber are typically 51.84 Mbps for UTP loops of 300 meters, 25.92 Mbps at 1,000 meters, and 12.95 Mbps at 1,500 meters. Upstream rates may fall into three classes, 1.6-2.3 Mbps, 19.2 Mbps, or equal to the downstream rate if permitted by class of service and available bandwidth.
There are several problems with current VDSL installations. First, since all packet routing takes place at a central office, the central office is a critical component to the system. If the central office fails, the entire area covered by the central office is without service. Further, the central office may become a bottleneck limiting the number of customers within the area that may be provided with VDSL service.
A second problem with current VDSL installations is the lack of ability to service all customers supported by the central office. Central offices are geographically located based on providing standard telephone services (POTS). In heavily populated areas, the coverage area of each central office may include more potential VDSL customers than the central office can support. In sparsely populated areas, potential VDSL customers are located at too great a distance from the central office to make VDSL services economically feasible.
A third problem with current VDSL installations is the ability to provide customers with a predictable level of service. The length, type, gauge, and quality of copper cabling connecting a VDSL customer and the central office is the predominant factor in determining the information rate available to the customer. Often, the copper loop was designed for only POTS service. Unshielded cable is typical. Wire of different gauges along the loop is not uncommon. Further, unterminated bridged taps are often spliced into the loop to increase the flexibility of the copper plant. Hence, neither the customer nor the service provider often knows the ultimate performance level until after the VDSL connection is made and tested.
Another promising technology is broadband delivery for video signals. A central office receives or generates video information for distribution to subscribers. This central office may be the same central office used for VDSL and POTS services or may be a separate central office for a given geographic area. The central office routes the video information to video distribution centers (VDCs) over distribution lines. Each VDC serves subscribers in a subset of the geographic area covered by the central office. Customer premises may be connected to the VDC over twisted pair, fiber or, more commonly, coaxial cable. Video signals may be received by a set-top box, a gateway, a decoder or transmitter incorporated into the receiver, or the like. Video signals may be broadcast from the central office, with each channel occupying bandwidth in the distribution line at all times. Video signals may also be switched, with only those signals requested by a subscriber being transmitted on the distribution line.
Many problems with video distribution networks are similar to difficulties experienced by VDSL systems. The central office presents both a critical component and a potential bottleneck. Because video distribution networks were typically designed for one-way distribution of video signals, they provide highly asymmetrical communication paths. Also, customer equipment designed for video display is often incompatible with digital data equipment.
What is needed is a communication system that provides high-speed information access for VDSL services, video signals, and the like. The system should make efficient use of bandwidth, allocating only the bandwidth necessary for a particular communication. The system should be flexible, permitting automatic addition and deletion of network components. The system should have distributed routing and service provisioning to prevent bottlenecks, permit scaling, and increase reliability and robustness. The system should support wireless communication, accommodating a wide variety of fixed, portable, and mobile user communication devices. The system should support high-speed symmetric and asymmetric communication for applications such as Internet access, video conferencing, real-time distributed document sharing, video-on-demand, and the like.